The invention relates to linear copolymers of carbon monoxide and an olefinically unsaturated compound and to a process for the preparation thereof.
EP-A-213671 discloses copolymers of carbon monoxide, ethene and one or more other olefinically unsaturated monomers (A), said copolymer consisting of units --CO--(C.sub.2 H.sub.4)--and --CO--(A)-- (A)-- whereby the units --CO--(C.sub.2 H.sub.4)-- and --CO--(A)-- are randomly distributed along the polymer chains. Hence, the copolymer is a linear alternating copolymer of carbon monoxide and ethene or another olefinically unsaturated monomer A on the other hand. The advantage of these polymers as compared to the high molecular weight linear alternating copolymers of carbon monoxide with ethene exclusively is that it has a lower melting point, enabling the melt processing of the polymer to take place at a lower temperature. This lower processing temperature in return reduces decomposition and discoloration of the polymer during processing. However, it is a disadvantage that at least one other olefinically unsaturated monomer beside ethene is necessary for preparing the polymers with reduced melting point, so that the total number of olefinically unsaturated monomers is at least two.
The polymers disclosed in EP-A-213671 have good mechanical properties, especially at elevated temperature, and have utility as engineering polymers.
Prior art references, such as U.S. Pat. No. 2,495,286 and G.B. A-1522942 disclose non-alternating copolymers of carbon monoxide and an aliphatic monoolefin, preferably ethene, prepared by using a free radical catalyst, thus accomplishing a free radical polymerization of the said carbon monoxide and aliphatic monoolefin. In these references, copolymers of carbon monoxide and ethene are described having molar ratios ethene to carbon monoxide varying from as low as 1.16:1 to as high as 20:1. The copolymers disclosed in said British patent specification have a molar ratio ethene to carbon monoxide of close to unity.
The ethene/carbon monoxide copolymers described in U.S. Pat. No. 2,495,286 and G.B. A-1522942 have melting points which are lower than those of corresponding perfectly alternating copolymers. However, it will be appreciated by persons skilled in the art that these copolymers do not have a linear structure but rather a branched structure due to the free radical polymerization mechanism. A drawback of polymers having a branched structure is their relatively high melt viscosity and that their melt processing may be seriously hampered. Moreover, well known disadvantages of free radical initiators are that they are storage unstable and that remnants of such initiators which can be detrimental to the polymer stability may be present in the prepared polymer.
It would be desirable to obviate the above-mentioned disadvantages associated with carbon monoxide based polymers.
EP-A-280380 discloses a process for producing linear alternating copolymers of carbon monoxide and one or more olefinically unsaturated compounds using catalyst compositions based upon a palladium compound and a phosphino-sulphonic acid ligand. The examples of this European application teach that said linear alternating copolymers can be prepared by applying in the polymerization mixture the olefinically unsaturated compounds at a molar ratio relative to the carbon monoxide of approximately 1:1.